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Clay Body Not Sticky Enough -- What To Do?


hanee

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In a recent quest to find a more local clay I picked up some of Sheffield's MGB body (coarse grog), as well as some ungrogged sheffield clay. There's a lot I like about this clay but am a bit shocked at how poorly it sticks to itself. I'm finding myself having to do things I've never done before, like wetting surface when building, in order to ensure that the clay is really joined and not merely laminated.

 

I was under the impression that earthenwares as a rule generally are going to have excellent plasticity and that the property of 'plasticity' generally refers also to adhesion. I would say the 'plasticity' is good in terms of pushing clay around, but the stickiness or adhesion is lacking almost completely, as far as adding on new pelletes of clay. Other clay bodies I've used in the past have never had such poor adhesion (including raku clays and other terracotta bodies). It's severely limiting.

 

So... what exactly causes a straightforward earthenware clay like sheffield's to be 'shorter' (if I'm using the term correctly) than other similar bodies I've used. Is it perhaps a lack of aging (this clay seems to be very freshly mixed, no mold spots or odor whatsoever) or is it inherent to their particular source material? Is there anything I can easily do to improve the stickiness? Oddly, the clay with more grog (MGB) adheres to itself *better* than the grogless version of the same body, which I thought was rather counter-intuitive. I've heard that stickier clay is going to have a higher shrink rate, but the raku and high grog terracottas I've used in the past were both sufficiently self-adhering and had low-shrink rate.

 

Meanwhile, I've dug some local clay (which I can't dig more of until spring) which is sticky to an extreme in its unprocessed state, and also far far stronger than the sheffield. I am guessing that much of this has to do with organic content in the 'wild' clay fattening it up and giving it such great plasticity? Also, interestingly enough, the 'wild' clay without any grog is stronger (in terms of supporting an outstretched arm or the like) than sheffield's MGB which has a high percentage of coarse grog and should therefore be vastly stronger.

 

I have other questions with regard to modifying sheffield's body or mixing my own, but will try to keep this thread concentrated on the question of stickiness. Is there something easy I can do to the sheffield clay to help the stickiness?

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I  would think it boils down to the additives /water content in the body.. I feel safer adding water or a little thick slip to make joins.. Always nice when you can just push or pinch to make joins when the clay is soft enough ... I have some clay that has additives in it and can be used for Raku, its ok but its leathery and hard to work with without water added. I was told that is how it comes and was not that old... 

 

Can you add some water to the body to soften it a little more? 

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Crusty, unfortunately I'm not making joins -- I'm a figure sculptor and model with many little bits of clay constantly being added. If I find that it wont accomodate my working methods, I will change the body or give it away if it's unchangeable. Not going to sacrifice the quality of my work for a misbehaving clay.

 

oldlady, I will try contacting them, but I'm betting this is a difference-of-application issue. Perhaps it would make a great throwing clay, but for sculpture, it's quite a pain. Tolerable for some depending on their working methods perhaps.

 

Neil, I've mostly used terracottas in the past, and also a decent amount of raku clays. I wouldn't call them particularly sticky but this clay is out of all my norms I'm used to. I don't really have experience with anything outside of terracottas, raku clays and a few general purpose school-clays back in college (stonewares mostly I believe).

 

As for moisture level, I don't think that's the factor here. I work with a wide, wide variety of moisture levels and reuse clay. I use it just as often out of a rubbermade of sprayed down scraps as I do out of the bag, I'm used to how most clays work in this range of conditions -- this one is out of all my norms and resists adhesionin in cases where every other clay body I've used, even not particularly plastic ones, would adhere fine.

 

As I said, the interesting thing is that the theoretically less-plastic *grogged* version adheres far better than *ungrogged*. Is there a simple explanation for that (perhaps the clay resists moisture and the grog helps to break up that resistance and carry moisture inward, increasing the bond)?

 

On reflection, I'm not that experienced with ungrogged clays so it may be some of the things I'm describing are a product of the lack of grog in the smooth body, and perhaps even in the coarse body, since this particular formulation uses all coarse and no fine grog which is different than most commmercial sculpture preparations I've used which contain a mix of both.

 

The counterpoint to this theory, though, is that, as I said, I have a native clay (also an earthenware most likely) that I have dug up that is almost as sticky as vaseline with no grog.

 

My instinct tells me that at least part of the problem is that this is just way too fresh of a mix, it just feels very sterile and bodiless compared to other clays I've used. It's hard to believe that their base is so radically different from all the other terracotta-sculpture bodies I've used. Perhaps tossing a bit of organic matter in and letting it rot a bit would improve things...

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  • 2 weeks later...

Hey,

On the topic of your natural clay, I'm not quite sure if its clay or

dirt with clay properties. I've talked with brick mfg engineers and when

they find à new quarry it has to be field tested. The field test is

getting a sample of clay about the size of an egg, and add enough water

to make it soft and pliable. Dirt won't do that. Then take the soft

clay and make a half inch thick coil and either wrap the coil around one

of your fingers, or tie an over hand knot with it. One of the engineers

checked out some of my soft clay at the lab and said the clay was too

brittle. Never understood how he came to that conclusion, but when vessels

made from that clay was fired, it could be pinched back into a powder

it was so brittle. I had to find another source at another river's bank.

Anyway, have fun testing your clay.

Alabama

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